1. Field of the Invention
The present invention relates to an impedance matching device. Specifically, the present invention relates to a small-sized impedance matching device with a small variation in quality and large-current tolerance.
2. Description of Related Art
In general, since the output impedance of a semiconductor element consisting of silicon (Si), gallium nitride (GaN) or the like is small, such a semiconductor element is often connected with a circuit for matching impedance when it is connected with an external circuit. Such a semiconductor element is connected with an impedance matching circuit to be capable of matching a characteristic impedance of an external circuit and transmitting the output from the semiconductor element.
The above-described impedance matching circuit is often constituted by a capacitor element and an inductor element consisting of a thin line of conductor connecting the capacitor element and a semiconductor element as described above (for example, metal wire) and the like. In such a configuration, the number of the components (i.e., a capacitor element and an inductor element) constituting an impedance matching circuit is large, the impedance matching circuit tends to be large-sized. However, since an impedance matching circuit is often mounted within a package for protecting a semiconductor element, an impedance matching circuit is required to be small-sized.
In addition, since the large number of components tends to complicate manufacturing process and increase production cost, it is required to suppress the number of components from such a viewpoint. Further, in the above-described configuration where a thin line connecting a semiconductor element and (a capacitor element in) an impedance matching circuit constitute an inductor as described above, the inductance of the inductor element varies when the length or curvature of the thin line varies. Accordingly, in order to achieve desired inductance, it is necessary to precisely control the length or curvature of the thin line, and this is also one of the causes complicating manufacturing process and increasing production cost (for example, refer to Patent Documents 1 and 2).
First, in order to reduce the size of an impedance matching circuit, it is supposed to configure the capacitor element and the inductor element constituting an impedance matching circuit as one component (i.e., an impedance matching device).
Strategies for configuring the capacitor element and the inductor element as one component as described above include forming a conductor pattern constituting the capacitor element, an inductor element, a wiring portion or the like within dielectric material and unifying them. For example, it is supposed to laminate green sheets comprising ceramic material with a conductor pattern screen-printed thereon, fire the resulting laminate, produce a ceramic electronic device comprising a capacitor element and an inductor element therein, and thereby achieve the downsizing of an impedance matching device.
However, in accordance with the method as described above, while downsizing of an impedance matching device can be achieved, it is difficult to form a conductor pattern with a sufficient thickness to achieve large-current tolerance since the conductor pattern is squashed or deformed when the green sheets with a conductor pattern screen-printed thereon are laminated. In addition, there are problems that a sharp edge portion resulting from the squash or deformation on lamination leads to concentration of electric current due to concentration of electric field and, especially when the thickness of a conductor pattern is large, a void between the green sheets adjacent to the conductor pattern leads to decrease in mechanical strength due to concentration of stress (for example, refer to Patent Documents 1 and 2).